In a very sensitive scanning calorimeter, five structural transitions of the human erythrocyte membrane can be seen over the temperature range from 45 degrees to 80 degrees centigrade. In some cases, the membrane components which participate in these transitions have been identified. For example, the spectrin complex unfolds in the A transition, bands 2.1, 4.1, and 4.2 are involved in the B1 transition, the cytoplasm domain of band 3 is a participant in the B2 transition while the transmembrane part of band 3 and associated lipids are involved in the C transition. The C transition has been shown to be very sensitive to the binding of specific inhibitors of anion transport such as DIDS, SITS, and pyridoxyl phosphate. It has likewise been shown that anion transport can occur only when the C region of the native membrane is intact and that the occurrence of all other transitions has no effect on transport capability. Current work is focusing on the effects of various proteases and phospholipases on anion transport and on the C transition. The nature of the structural changes which take place in these transitions is being studied with various techniques including calorimetry, light scattering, electron microscopy and thermal gel analysis.